1. Field of the Invention
The present invention provides a BIOARTIFICIAL kidney comprising (1) a filtration device comprising endothelial cells and pericyte cells and (2) a tubule processing device.
2. Background of the Invention
An implantable epithelial cell system derived from immortalized cells grown as confluent monolayers along the luminal surface of impermeable polymeric hollow fibers has been described as a first step for tubule functional replacement (Ip and Aebischer, Artificial Organs 13:58-65, 1989, incorporated herein by reference). Unfortunately, immortalized cells do not possess the full range of function of primary renal cells. Critical to development of functional renal tissue is the isolation and growth in vitro of primary cell lines. Primary cell lines should possess characteristics such that they exhibit a high capacity for self renewal. Preferably, the primary cell lines should possess stem cell-like characteristics such that they have the ability to differentiate under defined conditions into specialized cells having the correct structure and functional components of a physiologic kidney (Hall and Watt, Development 106:619-633, 1989; Potten and Loeffler, Development 110:1001-1020, 1990; Garlick et al., J. Invest. Dermatol. 97(5) :824-829, 1991; all incorporated herein by reference).
Prior to the contributions of the present inventors, primary cells could not be maintained for a sufficient time to make their use in bioengineering applications useful. The present inventors discovered methodology to isolate and grow renal tubule stem or progenitor cells from mammalian kidneys (U.S. Pat. No. 5,429,938; Humes and Cieslinski, Exp. Cell Res. 201:8-15, 1992; incorporated herein by reference).
Non-serum containing growth conditions were identified which select for tubule cells with a high capacity for self renewal and an ability to differentiate phenotypically, collectively and individually, into tubule structures in collagen gels. Genetic marking of the cells with a recombinant retrovirus containing the lac-Z gene and dilution analysis demonstrated that in vitro tubulogenesis arose from clonal expansion of a single genetically tagged progenitor cell. Thus, a population of tubule cells resides within the kidney which exists in a relatively dormant, slowly replicative state, but which retains a rapid potential to proliferate, differentiate and undergo pattern formation to regenerate the tubule epithelium of the lining of the kidney following severe ischemic or toxic injury.
Ex vivo studies on these renal tubule progenitor cells have demonstrated that a mixture of (i) TGF-.alpha. or EGF and (ii) retinoic acid (RA) can promote differentiation of these cells into renal tubules (Humes and Cieslinski, Exp. Cell Res. 201:8-15, 1992). Thus, a coordinated interplay between growth factors and retinoids appears to be required to induce pattern formation and morphogenesis. Using immunofluorescence microscopy, it has also been demonstrated that retinoic acid induces laminin A and B1 chain production in these cells and that purified soluble laminin can be completely substituted for retinoic acid in kidney tubulogenesis (Humes and Cieslinski, supra). Retinoic acid, as a morphogen, appears to promote pattern formation and differentiation by regulating the production of an extracellular matrix molecule.
Using this technology, the present inventors have described implantable bioartificial kidney devices (U.S. Ser. No. 08/133,436), which can replace renal function and as a result can circumvent the need for long-term dialytic therapy, would substantially benefit patients suffering from ESRD by increasing life expectancy, increasing mobility and flexibility, increasing quality of life, decreasing the risk of infection, and reducing therapy costs.
The present invention describes bioartificial devices with improved durability.